Most modern airplanes navigate by a combination of GPS (which uses satellites) and a system called intertial reference, and they also have the ability to communicate with ground stations and report their position automatically. In this case the question is whether and for how long those communications systems were actually operating. The airplane's course was "pinged" for awhile, then the communication stopped (maybe because the airplane ran out of fuel, which means the engines would stop running and their corresponding generators stopped producing power to run those systems). So far nobody knows why. As long as everything is working properly, systems like CPDLC (a satellite-based datalink system) do make it possible to keep track of where airplanes are, even when they are over an ocean and not in radar contact.